Portable battery power devices are increasingly common in modern life, e.g., mobile telephones, MP3 players, personal digital assistants (PDAs), notebook computers, DVD players, CD players, radios, televisions, and the like. However, the relatively short span of time before a fully charged battery becomes discharged and needs to be either recharged or replaced is a common problem in the operation of most battery powered devices To extend the “lifetime” of a battery's effective use, energy efficient circuitry is often included in battery powered devices.
Many battery powered devices include displays that provide information regarding the operation of the devices. Often, these displays are backlit to enable their use in low light environments. However, since backlit displays can consume a relatively large percentage of the available energy in the battery, relatively efficient LED driver solutions are preferred.
In the past, current regulated switch capacitor LED drivers have been employed to achieve a relatively optimized energy efficiency by switching between different gains. These different gains are switched to follow the voltage drop across the battery as it discharges. For example, when the battery is fully charged a gain of 1 is often selected because the battery's voltage is high enough to efficiently drive the LEDs. However, as the battery discharges and its voltage drops, a gain greater than 1 is then selected (1.5X for example) to boost the output of the LED driver above the battery's voltage. Previously, it has been difficult to determine the optimal point for this gain transition. Thus, it is with respect to these considerations and others that the present invention has been made.